Detailing the <scp>visco?elastic</scp> origin of <scp>thermo?mechanical</scp> training of twisted and coiled polymer fiber artificial muscles

Artificial muscles made be twisting and coiling polymer fibers provide outstanding performance. However, these materials show inconsistency in their non-loaded length that depends on thermo-mechanical history. Typically, this behavior has been treated by “training” the samples before any actuation testing. A change sample occurs during training but remains consistent subsequent heat/cool cycles at same applied load. In study, effect is investigated for a twisted coiled nylon yarn heated over two temperature ranges: 25–50°C 50–75°C. The was most obvious lower range, nearly absent higher range. When loaded below glass transition (Tg ~ 40°C) viscoelastic strain slowly rapidly released when first above Tg. net of heating through Tg after loading small because contraction due to offset expansion release strain. simple spring dashpot model developed changing only relaxation times it possible simulate observed phenomena.